Hydraulic apparatus

ABSTRACT

A swash plate pump in which the swash plate is adjustable in accordance with the pump delivery pressure so that piston stroke reduces as delivery pressure increases. A pair of piston-andcylinder servo units are provided to act oppositely on the swash plate, one of these servo units being fed with liquid at pump delivery pressure and the other servo unit being fed with liquid either at pump delivery pressure or a lower pressure depending on the position of a control valve. The control valve is contained within the said other servo unit and is subjected at one end to pump delivery pressure and at its opposite end to the load of a compression spring whereby to take up a position depending on pump delivery pressure. The pressure of liquid fed to the said other servo unit will be adjusted accordingly and the angle of the swash plate will be adjusted by the one or the other servo unit in accordance with pump delivery pressure.

United States Patent John Denis Smith Wolverhampton, England [21]Appl.No. 884,998

[72] Inventor [22] Filed Dec. 15, 1969 [45] Patented Oct. 12, 1971 [73]Assignee Boulton Paul Aircraft Limited Wolverhampton, Stafford, England[32] Priority Dec. 14, 1968 33] Great Britain [54] HYDRAULIC APPARATUSPrimary ExaminerLeonard H. Gerin Attorney-Young & Thompson ABSTRACT: Aswash plate pump in which the swash plate is adjustable in accordancewith the pump delivery pressure so that piston stroke reduces asdelivery pressure increases. A pair of piston-and-cylinder servo unitsare provided to act oppositely on the swash plate, one of these servounits being fed with liquid at pump delivery pressure and the otherservo unit being fed with liquid either at pump delivery pressure or alower pressure depending on the position of a control valve. The controlvalve is contained within the said other servo unit and is subjected atone end to pump delivery pressure and at its opposite end to the load ofa compression spring whereby to take up a position depending on pumpdelivery pressure. The pressure of liquid fed to the said other servounit will be adjusted accordingly and the angle of the swash plate willbe adjusted by the one or the other servo unit in accordance with pumpdelivery pressure.

SHEET 2 OF 3 DA M3.

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mmv wm mm/ mmmmwwmm w HYDRAULIC APPARATUS This invention relates tohydraulic apparatus and more particularly it relates to a variablestroke hydraulic pump.

In accordance with the present invention a variable stroke hydraulicpump comprises a rotary cylinder block, pump pistons extending fromcylinders in the block to engage a cam member such that the pistonsreciprocate during block rotation, a pair of servo piston and cylinderunits arranged to act by hydraulic pressure oppositely on the cam formoving the cam in the sense to vary piston stroke, a hydraulicconnection from the pump delivery extending directly to one servopiston, a hydraulic connection from the pump delivery extending to apilot valve in the second servo piston and a spring acting on the pilotvalve in opposition to the force developed by pump deliverypressurewhereby the pilot valve assumes a position in accordance with pumpdelivery pressure to connect the pump delivery pressure or a lowerpressure to act on the second servo piston to adjust the cam to aposition in accordance with the position assumed by the pilot valve.

The cylinders in the block may be parallel or inclined to the blockrotation axis and the cam may be a swash plate.

Preferably both servo units are located at equal distances from the tiltaxis of the swash plate and the area of the first servo piston issmaller than the area of the second servo piston.

One embodiment of the invention will now be particularly described withreference to the accompanying drawings, in which FIG. 1 is adiagrammatic view of an integrated unit including the variable strokepump,

FIG. 2 is a cross section through the variable stroke pump, and

FIG. 3 is a cross section through an accumulator forming part of theintegrated unit.

The described embodiment is intended for use on an aircraft as ahydraulic package control i.e. an integrated unit comprising electricdriving motor, hydraulic pump, hydraulic ram, liquid reservoir andcontrol valve whereby the package may be located at an appropriate placefor example in the wing of the aircraft for operation of a controlsurface, the power supply being through electric cables to the motor andthe control being by means of a convenient linkage system to the controlvalve.

In the embodiment, the hydraulic pump comprises a swash plate pump Imounted within a finned reservoir 2. An extension 3 of the reservoirlocates a reduction gear 4 and provides a mounting flange 6 for ahigh-speed electric motor 7. The hydraulic motor is secured to theextension 3 of the reservoir, and takes the form of a cylinder 8containing a double acting piston 9.

An accumulator structure 11 is also secured to the extension 3 of thereservoir.

The hydraulic pump comprises a rotary cylinder block 12 having cylinders13 extending parallel to the rotation axis and pistons 14 in thecylinders which extend from one end of the cylinder block to engage aswash plate 15. The swash plate is pivotally mounted by trunnions fortilt movement in order to vary the effective stroke of the pistons intheir cylinders during rotation of the cylinder block. The block ismounted for rotation on a valve 16 having a pair of main ports 17 and18. The port 17 is the inlet port to the pump and the port 18 is thehigh-pressure delivery port.

In order to adjust the angular setting of the swash plate a pair ofpiston and cylinder servo units 19 and 21 are provided. These two servounits are secured to the mounting structure 22 by which the whole pumpis carried within the reservoir 2 and are equidistantly spaced from theaxis of the swash plate trunnions 10. The servo unit 19 is a simplepiston and cylinder unit receiving high-pressure liquid directly fromthe high-pressure delivery port 18 through a passage 23 and actingdirectly on the swash plate 15 through a connecting rod 20.

The servo unit 21 is mounted on the opposite side of the pump to theservo unit 19 and basically comprises a piston 24 slidably mounted in acylinder 25. A connecting rod 30 connects the piston 24 to the swashplate 15. The thrusts exerted on the swash plate 15 by the twoconnecting rods 20 and 30 generate opposing torques on the swash plateabout the axis of the trunnions 10. The cross-sectional area of thepiston 24 over which liquid may act is larger than the cross-sectionalarea of the piston in servo unit 19.

A cylindrical pilot valve 27 is slidably mounted within the piston 24, aland 28 on the pilot valve controlling access of liquid into a workingspace 26 within which liquid may act on the piston 24 to urge it towardsthe swash plate. For this purpose a waisted portion 29 of the pilotvalve is adapted to connect a pressure port 31 or a reservoir port 32 tothe working space 26 depending on the axial piston position of the pilotvalve in the piston. At one end the pilot valve carries a small plunger33 which reacts directly against the piston 24, the pressure liquidhaving access to the one end of the plunger 33 so that the pressure ofliquid will tend to urge the pilot valve to the left as seen in thedrawing. The delivery port 18 of the pump is connected by a passage notshown to a grooved zone 34 around the piston 24 from which the liquidhas access both to the port 31 and to the plunger 33.

The end of cylinder 25 remote from the swash plate contains acompression spring 35 on which the pilot valve 27 is arranged to reactthrough the medium of a spring cap 36 whereby the axial position takenup by the pilot valve depends on the endwise force exerted on the pilotvalve by virtue of liquid pressure acting over the area of plunger 33 inopposition to the compression force exerted by the spring. The spring isa conventional coiled spring having a substantial rate so that for eachvalue of delivery pressure within a working range there is acorresponding position for the pilot valve.

In operation of the pump, rotational drive is applied to the shaft 37which in turn rotates the cylinder block 12 thus causing the pistons 14to reciprocate in their cylinders whereby liquid enters port 17 from thereservoir to be delivered as liquid at pressure from the port 18.initially such liquid at pressure will be supplied to both servo units19 and 21 and the servo piston 24 by virtue of its greater area willhold the swash plate 15 at its maximum inclination. As delivery pressurerises to a particular value the force exerted on the pilot valve 27 willcause it to move against the load of the spring 35. Such movement of thepilot valve will connect low pressure to the working space 26 and theswash plate 15 will be moved about its trunnions 10 by the force exertedby servo unit 19 until the connection to working space 26 is againclosed by the land 28 of pilot valve 27. Thus there is a unique relationbetween the pressure at the delivery port 18 and the angular setting ofthe swash plate.

Liquid is arranged to enter the port 17 from the reservoir through afilter 38.

Liquid delivered by the pump is arranged to pass through passages (notshown) in the portion 3 of the reservoir case to a control valve 39which will direct the liquid at pressure to one end or the other of thecylinder 8 so that movement of the piston 9 is in accordance with theposition selected for the control valve 39. Conventional feedbacklinkage may be provided in between the control valve 39 and the controldevice operated by the piston 9.

The accumulator assembly 11 supported from extension 3 comprises a pairof coaxial cylinders 41 and 42 internally separated by a flange 43. Theleft hand end of cylinder 41 is closed by a cap 44 formed as anextension from the portion 3 of the reservoir. The right-hand end of thecylinder 42 is closed by a cap 45. Within cylinder 41 a free piston 46is slidably mounted. The left-hand end of cylinder 41 forms thehigh-pressure accumulator and is connected through a passage 47 with thedelivery pressure from the port 18 of the pump. The right-hand end ofthe cylinder 41 is filled with an inert gas such as nitrogen under highpressure, the pressure being substantially equivalent to the deliverypressure from the pump. A piston rod 48 extends through a suitablysealed opening in the flange 43 from the cylinder 41 to the cylinder 42and in cylinder 42 is connected to a piston 49. The piston rod 48 andpiston 49 together form a differential piston. The cylinder 42 forms thelow-pressure accumulator. The passage 51 extending from the right-handend of the cylinder 42 connects to the reservoir 2. The left-hand end ofcylinder 42 is vented to atmosphere. The high pressure within cylinder41 exerts an endwise force on the rod 48 which is transferred to thepiston 49 to act on the liquid in the right-hand end of cylinder 42.Thus the pressure of the liquid in the right-hand end of cylinder 42will be smaller than the high pressure in cylinder 41 in proportion tothe-areas of the piston 49 and piston rod 48. For example it may bearranged that the pressure within cylinder 42 is one tenth of thepressure within cylinder 41. An indicator rod 52 is secured to thepiston 49 and extends through a suitably sealed opening in the end cap45 to form an external indicator of the quantity of liquid containedwithin the low-pressure accumulator. As liquid escapes from the systemby leakage, the indicator rod 52 will move further and further from theend cap 45, and in service regular inspection will establish the amountby which the indicator rod projects thereby to indicate whether or notit is necessary to put more liquid into the reservoir. Liquid may be fedinto the reservoir through a filler cap 53 mounted in a screw threadedfilling hole 54 on the reservoir. The cap 53 may contain a spring loadednonretum valve 55 arranged to vent liquid from the interior of thereservoir if the pressure should become excessively high. The extension3 also includes a highpressure relief valve 56 arranged to by pass thepump delivery back to the reservoir if the pressure rise in the pumpbecomes excessive.

in operation of the hydraulic unit described the electric motor will bedriven continuously at high speed and the pump shaft 37 will be drivenat a suitably reduced speed by virtue of the reduction gear 4. Liquid isinduced into the pump and delivered at pressure port 18, the actualpressure of the liquid so delivered being dependent on the flow rate ofliquid selected. Liquid flows at any instant when the control valve 39is adjusted to require a movement of the motor piston 9. Whenever thecontrol valve 39 is returned to a null position no delivery is requiredfrom the pump and its pressure will rise to a maximum moving the swashplate to an angle in which the stroke of the pistons is extremely small,being sufficient only to compensate for leakage from the pump to thereservoir. At this highest pressure within the range the accumulatorpiston 46 will be deflected to a substantial degree against the loadingof the inert gas in the cylinder 41. When the control valve 39 is movedto require movement of the motor piston 9, a flow of high-pressureliquid is immediately available by virtue of highpressure liquid withinthe high-pressure accumulator cylinder 41. Thus initial movement of thepiston 9 is effected by liquid delivered from the accumulator cylinder,the drop in pressure then enabling the swash plate of the pump to moveinto a position where stroke is given to the pistons and the pumpdelivers liquid at pressure. The whole reservoir and the inlet to thepump is maintained filled with liquid at low pressure as determined bythe pressure of the low-pressure accumulator and therefore no make uppump is required to maintain the pump primed with liquid. Liquid can belost from the unit described only through the positions where sealsisolate liquid at pressure from the ambient atmosphere.

The invention may be used with any kind of pump having a rotary cylinderblock and an adjustable cam member to adjust piston stroke and forexample could be equally applied to a radial cylinder pump.

In the illustrated embodiment the two servo piston and cylinder unitsare spaced at equal distances from the swash plate tilt axis but it iswithin the scope of the present invention to arrange that these twounits are unequally spaced from this tilt axis. In such a case therelative areas of the pistons of the two servo units would be arrangedso that the second servo piston when acted on by pump delivery pressurecould exert a greater torque on the swash plate than that exerted by thefirst servo piston.

I claim:

1. A variable stroke hydraulic pump comprising a rotary cylinder block,pump pistons extending from cylinders in the block to engage a cammember such that the pistons reciprocate during block rotation, a pairof servo piston and cylinder units arranged to act by hydraulic pressureoppositely on the cam for moving the cam in the sense to vary pistonstroke, a hydraulic connection from the pump delivery extending directlyto one servo piston, a hydraulic connection from the pump deliveryextending to a pilot valve in the second servo piston and a springacting on the pilot valve in opposition to the force developed by pumpdelivery pressure whereby the pilot valve assumes a position inaccordance with pump delivery pressure to connect the pump deliverypressure or a lower pressure to act on the second servo piston to adjustthe cam to a position in accordance with the position assumed by thepilot valve.

2. A variable stroke hydraulic pump as claimed in claim 1 wherein thecam is a swash plate.

3. A variable stroke hydraulic pump as claimed in claim 2 wherein thecylinders in the block are parallel to the block rotation axis.

4. A variable stroke hydraulic pump as claimed in claim 2 wherein bothservo units are located at equal distances from the tilt axis of theswash plate and the area of the first servo piston is smaller than thearea of the second servo piston.

5. A variable stroke hydraulic pump as claimed in claim 1 including alow pressure accumulator arranged to feed liquid at low pressure intothe pump and a high-pressure accumulator adapted to receive liquid athigh pressure from the pump.

6. A variable stroke hydraulic pump as claimed in claim 3 wherein bothservo units are located at equal distances from the tilt axis of theswash plate and the area of the first servo piston is smaller than thearea of the second servo piston.

7. A variable stroke hydraulic pump as claimed in claim 2 including alow-pressure accumulator arranged to feed liquid at low pressure intothe pump and a high-pressure accumulator adapted to receive liquid athigh pressure from the pump.

8. A variable stroke hydraulic pump as claimed in claim 3 including alow-pressure accumulator arranged to feed liquid at low pressure intothe pump and a high-pressure accumulator adapted to receive liquid athigh pressure from the pump.

9. A variable stroke hydraulic pump as claimed in claim 4 including alow-pressure accumulator arranged to feed liquid at low pressure intothe pump and a high-pressure accumulator adapted to receive liquid athigh pressure from the pump.

10. A variable stroke hydraulic pump as claimed in claim 6 including alow-pressure accumulator arranged to feed liquid at low pressure intothe pump and a high-pressure accumulator adapted to receive liquid athigh pressure from the pump.

1. A variable stroke hydraulic pump comprising a rotary cylinder block,pump pistons extending from cylinders in the block to engage a cammember such that the pistons reciprocate during block rotation, a pairof servo piston and cylinder units arranged to act by hydraulic pressureoppositely on the cam for moving the cam in the sense to vary pistonstroke, a hydraulic connection from the pump delivery extending directlyto one servo piston, a hydraulic connection from the pump deliveryextending to a pilot valve in the second servo piston and a springacting on the pilot valve in opposition to the force developed by pumpdelivery pressure whereby the pilot valve assumes a position inaccordance with pump delivery pressure to connect the pump deliverypressure or a lower pressure to act on the second servo piston to adjustthe cam to a position in accordance with the position assumed by thepilot valve.
 2. A variable stroke hydraulic pump as claimed in claim 1wherein the cam is a swash plate.
 3. A variable stroke hydraulic pump asclaimed in claim 2 wherein the cylinders in the block are parallel tothe block rotation axis.
 4. A variable stroke hydraulic pump as claimedin claim 2 wherein both servo units are located at equal distances fromthe tilt axis of the swash plate and the area of the first servo pistonis smaller than the area of the second servo piston.
 5. A variablestroke hydraulic pump as claimed in claim 1 including a low pressureaccumulator arranged to feed liquid at low pressure into the pump and ahigh-pressure accumulator adapted to receive liquid at high pressurefrom the pump.
 6. A variable stroke hydraulic pump as claimed in claim 3wherein both servo units are located at equal distances from the tiltaxis of the swash plate and the area of the first servo piston issmaller than the area of the second servo piston.
 7. A variable strokehydraulic pump as claimed in claim 2 Including a low-pressureaccumulator arranged to feed liquid at low pressure into the pump and ahigh-pressure accumulator adapted to receive liquid at high pressurefrom the pump.
 8. A variable stroke hydraulic pump as claimed in claim 3including a low-pressure accumulator arranged to feed liquid at lowpressure into the pump and a high-pressure accumulator adapted toreceive liquid at high pressure from the pump.
 9. A variable strokehydraulic pump as claimed in claim 4 including a low-pressureaccumulator arranged to feed liquid at low pressure into the pump and ahigh-pressure accumulator adapted to receive liquid at high pressurefrom the pump.
 10. A variable stroke hydraulic pump as claimed in claim6 including a low-pressure accumulator arranged to feed liquid at lowpressure into the pump and a high-pressure accumulator adapted toreceive liquid at high pressure from the pump.